Crystalline and amorphous sodium aluminosilicates are well known as detergency builders. Detergent compositions containing crystalline aluminosilicates are disclosed, for example, in GB 1 473 201 (Henkel). Amorphous aluminosilicates have also been proposed for use as detergency builders, for example, in GB 1 473 202 (Henkel), while GB 1 470 250 (Procter & Gamble) discloses detergent compositions containing mixed crystalline-amorphous aluminosilicates.
The crystalline sodium aluminosilicate zeolite A is the preferred material for detergents use because of its high capacity for taking up calcium ions from aqueous solution. Many other crystalline zeolites are known, for example, zeolite X, zeolite Y, zeolite P (also known as zeolite B) and zeolite C, and have found various uses outside the detergents industry. The use of some of these zeolites in detergent compositions has been suggested in the art: for example, EP 21 491A (Procter & Gamble) discloses detergent compositions containing a builder system which includes zeolite A, X or P(B) or mixtures thereof, and compositions containing hydrated zeolite B are disclosed in Examples VIII and IX. As far as commercially available detergent products are concerned, however, it is generally true to say that aluminosilicates other than zeolite A have not found favour as detergency builders because their calcium ion uptake is either inadequate or too slow. Zeolite A has the advantage of being a "maximum aluminium" structure containing the maximum possible proportion of aluminium to silicon--or the theoretical minimum Si:Al ratio of 1.0--so its capacity for taking up calcium ions from aqueous solution is intrinsically greater than those of zeolites X and P which generally contain a lower proportion of aluminium (or have a higher Si:Al ratio).
The structure and characteristics of zeolite P are summarised succinctly by Donald W Breck in his standard work, "Zeolite Molecular Sieves" (Robert E Krieger Publishing Company, Florida, first published 1974), on pages 72-73 and 168 of the 1984 edition. The term zeolite P actually embraces a series of synthetic zeolite phases, of which the commonest are the cubic (zeolite B or P.sub.c) and the tetragonal (zeolite P.sub.t). The typical oxide formula is: ##EQU1## wherein M is an n-valent cation, typically an alkali metal cation, most usually sodium; and the typical unit cell content is: ##EQU2##
In theory, therefore, the Si:Al ratio can range from 1.0 to 2.5, but according to William C. Beard, in "Molecular Sieve Zeolites", Adv. Chem Ser., 101, 237 (1971), the lowest value that has been observed is 1.1 (1.08).
U.S. Pat. No. 3,008,803 (Milton/Union Carbide) relates to the manufacture of crystalline zeolite P(B) and discloses a Si:Al ratio range of from 1.0 to 2.5. The average value is said to be about 1.75. This is consistent with the disclosure of DE 2 620 293A (Henkel, Degussa), which discloses the preparation of zeolite of type P, using destructured kaolin as starting material: sodium zeolite P having a Si:Al ratio ranging from 1.35 to 2.65 is disclosed. Materials having ratios in this range are intrinsically incapable of taking up sufficient quantities of calcium ions to be of interest as alternatives to zeolite A for detergency building.
Example 8 (column 5 line 60 to column 6 line 5) of the Milton patent describes the preparation of a material described as a type B(P) zeolite having a Si:Al ratio of 1.085. Repetition of that Example by the present inventors has failed to give a product as described, but instead gives mixtures having poor detergency building properties.
The present inventors have now succeeded in preparing samples of crystalline zeolite P having lower Si:Al ratios, ranging from 0.9 to 1.33, and have found these materials to be outstandingly effective as detergency builders. The materials with Si:Al ratios of 1.15:1 or below, which are particularly effective, were found to be characterised by an X-ray diffraction pattern not previously reported. Zeolites of the P type with Si:Al ratios below 1.07:1 are believed to be novel materials.